Manufacturing method for a spark plug
In a bond step, one end of ground electrode is bonded to a metallic housing. In a provisional bending step performed after the bonding step, an intermediate portion of the ground electrode is bent with a pressing die so that the other end of the ground electrode is opposed to a distal end surface of a center electrode. In a regular bending step performed after the provisional bending step, the position of the other end of the ground electrode is adjusted so as to adjust the dimension of a spark gap. Receiving dies are prepared for regulating a shift range of a distal end surface of the other end of the ground electrode in a direction perpendicular to an axial line of the center electrode in the process of bending the intermediate portion of the ground electrode in the provisional bending step. In the provisional bending step, the intermediate portion of the ground electrode is bent until the distal end surface of the other end of the ground electrode is brought into contact with the receiving dies.
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This invention relates to a manufacturing method for a spark plug installed in an internal combustion engine of an automotive vehicle or the like.
A conventional spark plug has a columnar center electrode insulated and held inside a metal housing and a ground electrode having one end being bonded to the housing, wherein the ground electrode is bent at its intermediate portion so that the other end of the ground electrode is opposed to a distal end surface of the center electrode.
A spacer is used for regulating a bending amount in a provisional bending step of the ground electrode, so that a spark gap is suppressed or regulated within a predetermined range at the end of the provisional bending step (refer to Japanese Patent Application Laid-open No. 2000-164320).
However, according to the manufacturing method disclosed in the above-described prior art document, the protruding amount of a distal end surface of the other end of the ground electrode is not constant.
In other words, the unevenness of the protruding amount increases. This is an ignition property deteriorating factor of the spark plug. In this specification, the “protruding amount” is an overhang of the distal end surface of the other end of the ground electrode with respect to the axial line of the center electrode in a direction perpendicular to the axial line of the center electrode.
SUMMARY OF THE INVENTIONIn view of the above-described problems, the present invention has a first object to improve dimensional accuracy of the protruding amount. Furthermore, the present invention has a second object to improve dimensional accuracy of both a spark gap and the protruding amount.
In order to accomplish the above and other related objects, the present invention provides a method for manufacturing a spark plug including a columnar center electrode insulated and held inside a metal housing and a ground electrode having one end being bonded to the housing. The ground electrode is bent at its intermediate portion so that the other end of the ground electrode is substantially perpendicular to an axial line of the center electrode. The other end of the ground electrode is opposed to a distal end surface of the center electrode via a predetermined spark gap. The manufacturing method of this invention includes a bonding step, a provisional bending step, and a regular bending step. The bonding step is performed to bond one end of the ground electrode to the housing. After the bonding step, the provisional bending step is performed to bend an intermediate portion of the ground electrode with a pressing die so that the other end of the ground electrode is opposed to a distal end surface of the center electrode. After the provisional bending step, the regular bending step is performed to adjust a position of the other end of the ground electrode so as to adjust the dimension of the spark gap. The receiving dies are prepared for regulating a shift range of a distal end surface of the other end of the ground electrode in a direction perpendicular to the axial line in the process of bending the intermediate portion of the ground electrode in the provisional bending step. And, in the provisional bending step, the intermediate portion of the ground electrode is bent until the distal end surface of the other end of the ground electrode is brought into contact with the receiving dies.
According to this invention, the receiving dies regulate the protruding amount of the other end of the ground electrode in the provisional bending step. Thus, it becomes possible to improve the dimensional accuracy of the protruding amount at the end of the provisional bending step.
Preferably, the position of the pressing die in the axial line in the provisional bending step is determined with reference to the position of the distal end surface of the center electrode.
According to this method, it becomes possible to reduce the unevenness in the size of the spark gap during the provisional bending step. Furthermore, it becomes possible to reduce the dimensional accuracy of both the spark gap and the protruding amount at the end of the provisional bending step.
Preferably, the provisional bending step is performed in a condition that both sides of the ground electrode are clamped by the receiving dies when the ground electrode is seen from the axial line.
According to this method, the receiving dies prevent the ground electrode from shifting in the lateral direction of (i.e., a direction of the side surfaces of) the ground electrode. Thus, it becomes possible to accurately perform the provisional bending step.
Preferably, the position of the distal end surface of the center electrode is measured by image processing.
According to the above-described prior art document, the position of the distal end surface of the center electrode is measured by laser. However, laser is disadvantageous in that the depth of field is shallow. The measurement based on the laser is adversely influenced by surface conditions (flatness, cutout, etc.) of the distal end surface of the center electrode or unevenness in the position of the distal end surface of the center electrode. Thus, the measurement based on the laser is inaccurate.
On the other hand, according to the above method, the position of the distal end surface of the center electrode is measured by image processing. Thus, it becomes possible to perform accurate measurement without being influenced by the surface conditions of the distal end surface of the center electrode or by the unevenness in the position of the distal end surface of the center electrode.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description which is to be read in conjunction with the accompanying drawings, in which:
A preferred embodiment of the present invention will be explained hereinafter with reference to attached drawings.
In
The ground electrode 13 is straight at the time it is bonded to the housing 10 as shown in
As shown in
In the provisional bending step, the image processing apparatus 3 measures the position of the distal end surface 12a of center electrode 12 based on the image data and determines an operation amount of a provisional bending apparatus 4 (described later in detail) with reference to the position of the distal end surface 12a of center electrode 12. Thus, the image processing apparatus 3 controls the operation of the provisional bending apparatus 3.
Furthermore, in the regular bending step, the image processing apparatus 3 measures the dimension of the spark gap G based on the image data, and determines the operation amount of a regular bending apparatus 5 (described later in detail) based on the measured amount of the spark gap G, thereby controlling the operation of the regular bending apparatus 5.
Next, the provisional bending apparatus 4 will be explained with reference to
The second motor 42 is installed on the holder 43. The second motor 42 drives or actuates a pressing die 44 and a cam plate 45 so as to move together in the back-and-forth direction. When the pressing die 44 is moved toward the spark plug 1 (i.e., forward), the pressing die 44 is brought into contact with the ground electrode 13 to bend the intermediate portion of the ground electrode 13 (refer to
A pair of link levers 46 and 47 swing in accordance with the shift movement of the cam plate 45. The cam plate 45 has a pair of cam grooves 45a. Pins 46a and 47a, provided at one end of respective link levers 46 and 47, are slidably inserted into the cam grooves 45a of the cam plate 45. Pivot shafts 46b and 47b, provided at an intermediate portion of respective link levers 46 and 47, are rotatably supported by the holder 43. Receiving dies 48 and 49 are attached to the other end of respective link levers 46 and 47.
Two receiving dies 48 and 49 cooperatively regulate the shape of the ground electrode 13 during the provisional bending operation. To this end, as shown in
In accordance with a shift movement of the pressing die 44 and the cam plate 45 from the bending start position (i.e., the position shown in
In this case, at the time the pressing die 44 is brought into contact with the ground electrode 13, i.e., at the time the operation of bending the ground electrode 13 is started, two receiving dies 48 and 49 are positioned most closely. Two positioning portions 48a and 48b of the first receiving die 48 are brought into contact with two positioning portions 49a and 49b of the second receiving die 49.
Furthermore, in the condition that two receiving dies 48 and 49 are positioned most closely, both side surfaces 13d (refer to
Next, the regular bending apparatus 5 will be explained with reference to
Next, the processes for manufacturing the ground electrode 13 performed by the above-described manufacturing apparatus will be explained.
<Bonding Step>
First of all, the ground electrode 13 extending straight is bonded to the housing 10. Then, the insulator 11 and the center electrode 12 are assembled in the housing 10 to obtain the spark plug 1 having the arrangement shown in
<Provisional Bending Step>
After the above-described bonding step, as shown in
Next, the image processing apparatus 3 calculates respective target positions of pressing die 44 and two receiving dies 48 and 49 in the up-and-down direction with reference to the position of the distal end surface 12a of center electrode 12. These target positions are determined so that the dimension of the spark gap G becomes equal or close to a predetermined value after the provisional bending operation. Then, by controlling the operation of the first motor 41, the pressing die 44 and two receiving dies 48 and 49 are shifted to their target position in the up-and-down direction (refer to
Next, the image processing apparatus 3 controls the operation of second motor 42 to shift the pressing die 44 and the cam plate 45 forward to the predetermined positions. The link levers 46 and 47 rotate in accordance with the shift movement of the pressing die 44 and the cam plate 45. Two receiving dies 48 and 49 approach to each other in accordance with the rotations of the link levers 46 and 47. At the time the pressing die 44 is brought into contact with the ground electrode 13, two receiving dies 48 and 49 are positioned most closely.
After the pressing die 44 is brought into contact with the ground electrode 13, the pressing die 44 further shifts forward. At this moment, the intermediate portion of ground electrode 13 are clamped between the intermediate portion positioning portion 48a of first receiving die 48 and the intermediate portion positioning portion 49a of second receiving die 49. Thus, the ground electrode 13 is bent at its intermediate portion being guided by the surfaces of the receiving dies 48 and 49. The opposed portion 13b of ground electrode 13 formed through this bending operation extends substantially perpendicularly to the axial line X and is opposed to the distal end surface 12a of center electrode 12.
In this case, as shown in
Furthermore, the side surfaces 13d of the ground electrode 13 are clamped between the opposed surface 48c of first receiving die 48 and the opposed surface 49c of second receiving die 49. This prevents the ground electrode 13 from shifting in the direction of both side surfaces 13d. The direction of both side surfaces 13d is a right-and-left direction shown in
<Regular Bending Step>
After the above-described provisional bending step, the dimension of spark gap G is adjusted by using the regular bending apparatus 5 shown in
First, after accomplishing the provisional bending step, the dimension of spark gap G is measured based on the image data obtained from the CCD camera 21 (Step S10). Then, the stop position of the electric motor 51 for lowering the working head 52 is calculated based on the measured value of the spark gap G (Step S11).
Next, the electric motor 51 is operated until it reaches the stop position. In accordance with the operation of the motor 51, the working head 52 is lowered to the predetermined position (indicated by an alternate long and two short dashes line in
Next, the electric motor 51 is rotated in the opposite direction to raise the working head 52 (Step S13). The dimension of spark gap G after accomplishing the regular bending step is measured (Step S14). Then, it is judged as to whether or not the measured value of spark gap G is within an allowable range (Step S15). When the measured value of spark gap G is smaller than the allowable range, this spark plug is excluded as a defective product (Step S16). On the other had, when the measured value of spark gap G is larger than the allowable range, the flow of control processing returns to the step S11 to perform readjustment of spark gap G.
According to the above-described embodiment, the distal end surface positioning portion 48b of first receiving die 48 and the distal end surface positioning portion 49b of second receiving die 49 cooperatively regulate the protruding amount L of during the provisional bending operation. Thus, it becomes possible to improve the dimensional accuracy in adjusting the protruding amount L in the provisional bending.
Furthermore, the target positions of pressing die 44 and two receiving dies 48 and 49 are determined so that the dimension of the spark gap G after the provisional bending operation becomes equal or close to the predetermined value. This makes it possible to reduce the unevenness of spark gap dimension caused in the provisional bending. Thus, it becomes possible to improve the dimensional accuracy of spark gap G at the time the provisional bending operation is accomplished.
Furthermore, the opposed surface 48c of first receiving die 48 and the opposed surface 49c of second receiving die 49 clamp the side surfaces 13d of ground electrode 13, so as to prevent the ground electrode 13 from shifting in the direction of the side surfaces 13d. Thus, it becomes possible to accurately perform the provisional bending operation.
Furthermore, the position of the distal end surface 12a of center electrode 12 is measured by image processing. This makes it possible to perform accurate measurement without being influenced by the surface conditions of the distal end surface 12a of center electrode 12 or the unevenness in the position of the distal end surface 12a of center electrode 12.
Claims
1. A method for manufacturing a spark plug comprising a center electrode insulated and held inside a housing and a ground electrode having one end being bonded to said housing, wherein said ground electrode is bent at its intermediate portion so that an axial line of said ground electrode at the other end thereof is substantially perpendicular to an axial line of said center electrode, and said other end of said ground electrode is opposed to a distal end surface of said center electrode via a predetermined spark gap, said manufacturing method comprising:
- a bonding step of bonding one end of said ground electrode to said housing;
- a provisional bending step, performed after said bonding step, of bending an intermediate portion of said ground electrode with a pressing die so that the other end of said ground electrode is opposed to the distal end surface of said center electrode; and
- a regular bending step, performed after said provisional bending step, of adjusting a position of the other end of said ground electrode so as to adjust the dimension of said spark gap, wherein
- a protruding amount of a distal end surface of said other end of said ground electrode in a direction perpendicular to said axial line of said center electrode is regulated by a receiving die in the process of bending the intermediate portion of said ground electrode in said provisional bending step, wherein the protruding amount is defined as a distance between said distal end surface of said ground electrode and an imaginary axial extension of said center electrode, measured in said direction perpendicular to said axial line of said center electrode,
- in said provisional bending step, said intermediate portion of said ground electrode is bent until said distal end surface of said other end of said ground electrode is brought into contact with said receiving die, and
- said distal end surface of said ground electrode, in contact with the receiving die, is protruded from said center electrode by said protruding amount.
2. The manufacturing method for a spark plug in accordance with claim 1, wherein the position of said pressing die in said axial line in said provisional bending step is determined with reference to the position of said distal end surface of said center electrode.
3. The manufacturing method for a spark plug in accordance with claim 1, wherein said provisional bending step is performed in a condition that both sides of said ground electrode are clamped by said receiving dies when said ground electrode is seen from said axial line.
4. The manufacturing method for a spark plug in accordance with claim 2, wherein the position of said distal end surface of said center electrode is measured by image processing.
Type: Grant
Filed: Oct 16, 2003
Date of Patent: May 16, 2006
Patent Publication Number: 20040078972
Assignee: Denso Corporation
Inventor: Takeshi Hanai (Kuwana)
Primary Examiner: Marc Jimenez
Assistant Examiner: Christopher Agrawal
Attorney: Nixon & Vanderhye PC
Application Number: 10/685,602
International Classification: H01T 21/02 (20060101);